1. Field of the Invention
The present invention relates to a device for interferential distance measurement.
2. Discussion of Related Art
One such device is known from German Patent Disclosure DE 10 2007 016774 A1, for example. It includes a light source and a scanning element or scanning plate in the form of a transparent glass plate. A splitter is disposed on the glass plate and splits the beam, emitted by the light source, into at least one measurement beam and at least one reference beam. A reflector is also provided spaced apart in the direction of the propagation direction of the beams. Via one or more detector elements, the resultant interference signals are detected. The interference signals occur here as a result of the superposition of a measurement beam and a reference beam. The measurement beam is propagated in the direction of the reflector and is reflected back from there to the scanning plate. The reference beam is guided solely in the scanning plate and is finally brought into interfering superposition with the measurement beam. From the interference signals thus obtained, the distance between the scanning plate and the reflector, and the changes in distance between these components, can be ascertained in a known manner. Such devices may be used for instance in semiconductor production equipment, for instance in order to make additional information available with regard to possible tilting, along with the two-dimensional displacement information with regard to a wafer table obtained via conventional position measuring instruments. A disadvantage of the known device from DE 10 2007 016774 A1 is now that the measurement beam and reference beam travel different travel lengths in various media; in particular, the reference beam is propagated nearly exclusively in the scanning plate. If therefore fluctuations in the wavelength of the radiation furnished by the light source result from changes in temperature, pressure or humidity for the measurement beam that is propagated in air, the consequence are errors in the distance determination, since precisely this wavelength functions as the measurement standard.